Factors Affecting the Energy Delivered to Simulated Class I and Class V Preparations

On 2010年08月11日 by Richard B.T. Price Resource：JCDA.com Hits：

Introducd：Purpose: To determine the effect of operator, curing light and preparation location, as well as any correlations among these variables, on the amount of light energy delivered to simulated cavity preparations. Materials and Methods: Each of 10 dentists and 10 fourth-year dental students light-cured a Class I preparation in tooth 26 and a Class V preparation in tooth 37 in a dental mannequin head. The operators exposed each preparation for 10 seconds with each of 3 LED-based curing lights (Bluephase G2 on high power, Demi and VALO on standard power). Each operator also used the VALO unit in the plasma mode for 2 sequential 3-second curing cycles. For each combination of operator, curing light and preparation, the irradiance (mW/cm2) received at the base of the preparation was measured with a laboratory-grade spectroradiometer, and software was used to calculate the energy density delivered in real time. The statistical analysis included 3-way analysis of variance (ANOVA) and the Fisher protected least significant difference (PLSD) test for post hoc pairwise comparisons. Results: There was a large qualitative and quantitative variation in the irradiance delivered to the preparations by each operator. Three-way ANOVA showed no statistically significant differences between dentists and dental students in terms of the amount of energy delivered (p = 0.90). However, there were statistically significant differences in energy delivered by the various curing lights (p < 0.001) and between the 2 preparation locations (p < 0.001). According to the Fisher PLSD test for post hoc pairwise comparison of means, the VALO unit used in the plasma mode for two 3-second curing cycles delivered the most energy (16.4 ± 3.1 J/cm2) to the Class I preparation, and the same light used for 10 seconds in the standard mode delivered the least amount of energy (9.9 ± 2.4 J/cm2) (p < 0.001). For the Class V preparation, the VALO unit used in the plasma mode for two 3-second curing cycles delivered the most energy (12.5 ± 4.0 J/cm2), and the Demi unit, used for 10 seconds, delivered the least energy (7.4 ± 2.5 J/cm2). Conclusions: The energy delivered by a curing light to a preparation in a simulated clinical environment was affected by the operators light-delivery technique, the choice of curing light and the location of the preparation.

Introduction

The success of resin restorations depends on many factors, including the technical difficulty of the procedure, the degree of moisture control, the effects of shrinkage during polymerization, the type of resin, the porosity of the resin and how well the resin is cured. Four variables affect the extent to which a resin is polymerized (cured) within the tooth: operator technique, choice of curing light, location of the restoration and type of resin used. A recently developed device called Managing Accurate Resin Curing (MARC; BlueLight analytics inc., Halifax, NS) takes all 4 of these variables into account, measuring both the irradiance and the energy received by a simulated preparation in a mannequin head.¹

The irradiance values for commercially available curing lights rang

e from 300 to 4000 mW/cm², but it is not the irradiance that determines how well a resin is cured. Instead, adequate polymerization of composite resins correlates strongly with the irradiant energy delivered to the restoration. The energy density (J/cm²) received by the resin is the mathematical product of irradiance (mW/cm²) and exposure time. Thus, after a 10-second exposure, a commercial curing light delivering 1000 mW/cm² would deliver an energy density of 10 J/cm². Resin manufacturers provide minimum curing times and irradiance levels and thus define the minimum energy requirements for their resins. Depending on the brand and shade, these have been reported to range from 6 to 24 J/cm² for a 2-mm increment of dental resin.^1-7 Because of wide variation in the irradiance of curing lights and the differing energy requirements of resins, the required exposure times vary widely. In addition, the light intensity of the majority of curing units decreases over clinically relevant distances; therefore, as the distance to the resin increases, longer exposure times may be needed to deliver the required energy to the restoration.^8-11 This reduction in irradiance with increasing tip distanc

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